1. Field of The Invention
The present invention relates to an expressing plate for a filter press.
2. Description of the Prior Art
In an expressing filter plate using flexible expressing sheets, generally, the flexible expressing sheets are bonded to the opposite surfaces of a core plate along the peripheral edge and filter cloth is placed thereon to cover the same. In the filtering operation, an expressing fluid is fed in between the core plates and the expressing sheets to expand the expressing sheets to express and filter a raw liquid. The filtrate is discharged into the outside through openings in the lower portions of the expressing sheets and through holes in the core plate continuous with said openings.
After said expression, the expressing sheets contract under their own contracting force, so that the fluid forced in between said sheets and the core is discharged. The expressing sheets develop deformation due to elongation strain each time said filtering operation is repeated. Such deformation upsets the sealed condition between the expressing sheets and the core plate at the expressing fluid inlet holes and filtrate discharge ports, causing misalignment between the discharge ports in the core plate and the openings in the expressing sheets. In extreme cases, said holes would be closed.
If said openings are closed, the filtrate remains in the filtrate chambers, with its pressure cooperating with the pressure of the pressurized fluid held between the expressing sheets and the core plate to develop an abnormal high pressure in the filtrate chambers, leading to fracture of the parts. Accordingly, there has been a disadvantage that it is impossible to increase the expressing pressure for filtering operation.
An invention intended to provide a solution to the technical problem described above is found in U.S. Pat. No. 4,235,721 wherein as a means for fixing an expressing sheet to an opening in a core plate, a reinforcing patch plate is applied to a filtrate outlet port.